As a liquid transfer machine, a pump is classifiable from the point of view of working principles into a turbopump, a positive displacement pump, and a special pump.
The turbopump has a casing and a vaned rotor (called “impeller”) disposed therein cooperatively defining channels for liquid to flow, and is adapted for the impeller's rotation to provide liquid in the channels with a pumping head. The head-provided liquid is called “pumped liquid”.
For conventional turbopumps, fundamental impeller types and typical characteristics are listed in Table-1 below.
TABLE 1Fundamental Impeller Types and Typical CharacteristicsTypesCentrifugalMixed flowAxial flowOutflow directionRadialDiagonalAxialHead providerCF*1CF*1 + VPF*2VPF*2Head, HHighModerateLowDelivery, QSmallModerateLargeSpecific speed, Ns100~150350~11001200~2000Meridian contourC1, C2 (FIG. 26) C3~C6 (FIG. 26)C7 (FIG. 26)*1CF = centrifugal force, *2VPF = vane's pumping force
As shown in the Table-1, the impeller of turbopump is classifiable into three fundamental types according to the outflow direction of pumped liquid. In other words, a centrifugal type has an outflow direction substantially perpendicular to the axis of rotation, which is radial; a mixed flow type has an outflow direction diagonal to the axis of rotation; and an axial flow type has an outflow direction substantially parallel to the axis of rotation. In the axial flow type, liquid flows in an axial direction, receiving axial pumping forces from the vanes of the impeller, and obtaining a head principally therefrom. In the mixed flow type, flowing liquid has radial moving components and receives commensurate centrifugal forces, as well as pumping forces from vanes, thereby obtaining head. In the centrifugal type, liquid flows in radial directions, receiving centrifugal forces, and obtaining head principally therefrom. Accordingly, in general, the centrifugal type has high head, but small delivery. However, the axial flow type has low head, but large delivery. The mixed flow type falls somewhere in between.
In this respect, the outflow direction of pumped liquid depends change in the radial direction of channels. Radial changes in channels are easily understood by observing a meridian map of the channels, that is, a meridian channel (hereafter referred to as “M-channel”).
The Meridian map is a rotational mapping of a body of rotation onto a meridian plane (i.e., a plane that includes the axis of rotation). In the case of turbopump, it appears as a meridian contour (hereafter sometimes referred to as “M-contour”), where the impeller and a casing that constitutes a shroud of one or more channels have their inside contours (which actually extend in a circumferential direction with their curvilinear changes) circumferentially projected on a plane including an axis of the impeller, there being manifested an angular change.
The M-contour can be generally specified by a non-dimensional parameter called “specific speed”. The specific speed corresponds to a required number of revolutions (rpm) of the pump for delivery of a unit flow rate (1 m3/min) of liquid pumped to a unit head (1 m). Letting Q be a delivery flow (m3/min) at a designed number of revolutions N (rpm) of a target pump, and H be a total head (m), the specific speed Ns of the pump can be expressed such that:Ns=N·Q1/2/H3/4.
For conventional turbopumps, FIG. 26 shows a relationship between the specific speed Ns and exemplary M-contours MC1˜MC7. As will be apparent from FIG. 26, for the centrifugal type (MC1, MC2) to be large in H and small in Q, the Ns can be as small as ranging approx. 100 to approx. 150, however for the axial flow type (MC7) to be small in H and large in Q, the Ns can be as large as ranging approx. 1200 to approx. 2000. For the mixed flow type (MC3˜MC6), the Ns can decrease from approx. 550 to approx. 350, as the outflow direction of pumped liquid approaches (MC3←MC4) a radial direction, or on the contrary, can increase from approx. 600 to approx. 1100, as the outflow direction of pumped liquid approaches (MC5→MC6) an axial direction. M-contours, e.g. MC1 and MC2, of impellers of the centrifugal type define M-channels, e.g. mp1 and mp2, extending in a radial direction at their delivery ends. M-contours, e.g. MC3˜MC6, of impellers of the mixed flow type define M-channels, e.g. mp3˜mp6, diagonal to the axis of rotation at their delivery ends. M-contours, e.g. MC7, of impellers of the axial flow type define M-channels, e.g. mp7, substantially parallel to the axis of rotation at their delivery ends.
The configuration of such conventional turbopumps will be described below. The turbopump will be called “axial flow pump” when provided with an axial flow type of impeller, “mixed flow pump” when provided with a mixed flow type of impeller, or “centrifugal pump” when provided with a centrifugal type of impeller.
Japanese Patent Application Laying-Open Publication No. 7-247984 has disclosed a conventional axial flow pump. This axial flow pump is configured with an axial flow impeller provided in a cylindrical casing, to have large delivery and low head. This impeller has an M-channel widened at the suction end to reduce the net positive suction head.
Japanese Patent Application Laying-Open Publication No. 10-184589 has disclosed a conventional mixed flow pump. This mixed flow pump is configured with a mixed flow impeller provided in a drum-shaped pump casing, so that liquid receives the impeller's pumping forces and centrifugal forces, thereby obtaining head. This impeller has gap narrowing members fixed to vanes thereof for reducing leakage of liquid.
Japanese Patent Application Laying-Open Publication No. 7-91395 has disclosed a conventional centrifugal pump. This centrifugal pump has an impeller configured with an M-channel lying along the axial direction of a spindle at the suction end, moderately curving on the way, and extending in a radial direction at the delivery end. With its centrifugal effect, it is well adapted for pumping water to a high or distant site. The rotation shaft is made short by employing a stationary pressure type bearing in liquid.
Japanese Patent Application Laying-Open Publication No. 11-30194 has disclosed another conventional centrifugal pump. This centrifugal pump is configured with an inducer added at the suction end of a centrifugal impeller, and has good suction performance. By the provision of a balance disc at the delivery end, the impeller has balanced thrust forces acting thereon.
The axial flow pump, having a relatively large specific speed, can have an extremely large delivery flow. It however is unable to raise the head, because cavitation occurs at high heads.
The mixed flow pump, having a medium specific speed, can have a higher head than the axial flow pump. It however is unable to have a large delivery flow due to cavitation.
The centrifugal pump, having a relatively small specific speed (about 100˜300), can have a higher head than the mixed flow pump. It however is subject to an ever smaller delivery flow due to cavitation.
The centrifugal impeller may have an increased inlet diameter for the suction performance to be successfully enhanced to provide the centrifugal pump with a to some extent improved anti-cavitation performance, but with a resultant failure to achieve a sufficient delivery flow.
In this respect, at the suction end of the centrifugal impeller, an inducer configured with two to four spiral vanes may be successfully added, to sufficiently enhance the suction performance of centrifugal pump.
It however is necessary for conventional centrifugal pumps to have six or more vanes in order to achieve a sufficient delivery flow, while securing the high head.
As a solution, there has been provided a communication path commonly interconnecting the respective channels of an inducer and respective channels of an impeller, allowing fluid from the inducer to be evenly distributed over the impeller.
As a result, foreign matter in the fluid sometimes got tangled around the communication path.
This invention has been made in view of such points. It therefore is an object of the invention to provide a turbopump adapted for a sufficient delivery flow to be achieved with a high head secured, as well as for the passability of foreign matter to be good.